Stability and degradation of PEO20PPO70PEO20 triblock copolymers in mesostructured silica

Abstract

Organic-inorganic hybrid mesostructured silicas are prepared, without stirring (at pH 0.0) and with stirring (at pH 0.6) to obtain isolated and gyroidal-like attached silica grains with incorporated triblock P123 poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) copolymers. Selected hybrids are submitted to various thermal and aging treatments for studying hydrolysis and oxidation of PEO and PPO chains. Two complementary spectroscopic techniques are used. Near-Infrared (NIR) with measurements performed in diffuse reflectance as well as 1 H and 13 C liquid-and solid-state Nuclear Magnetic Resonance (NMR) to study mobility and stability of PEO and PPO chains. With precipitated fresh hybrids, the ratio of PEO over (PEO + PPO) units is lower (%30 ± 5 %) than in theory. This ratio also decreases depending on temperature when a hydrothermal treatment is applied. An acidic hydrolysis involving both PEO and PPO chains, with generated fragments eliminated by washing with water and/or synthesis liquor, is then demonstrated. For comparison, another hybrid obtained by spray drying via Evaporation Induced Self Assembly mechanism, is also studied. Its NMR signals are much more stable than those of the samples prepared by precipitation. Depending on aging time, thermal history and materials processing, the textural properties and template decomposition inside mesostructured silica are found significantly different. The influence of the hydrolysis and oxidation of the template onto final materials texture is likely to be as important as processing conditions.

Assessing mesoscopic organization in copolymer-templated silica hybrid films via solid-state nuclear magnetic resonance

“…Top view respectively. Our assignment is in agreement with literature data [26]. A dramatic increase in resolution accompanies the increase of copolymer concentration, thus translating the effect of mesostructuration.…”

Amorphous mesostructured zirconia with high (hydro)thermal stability

“…This broadening can indicate the presence of several conformations of PEO units or a decrease in mobility. 58 Moreover, an additional resonance, barely observable on the 13 C MAS NMR spectrum, is clearly detected at 65.7 ppm thanks to the CPMAS NMR experiment. This resonance could correspond either to propanol or to propoxy groups coming from zirconium n-propoxide (Zr-Opr) that was not fully hydrolyzed during the synthesis, or to a mixture of both.…”

“…4A and B) are slightly broadened except the resonance assigned to the CH 2 of PEO species that is drastically broadened by the water removal as already reported in the literature. 58 Indeed, dehydration of PEO moieties obviously reduces their mobility. This again suggests low interaction with the zirconia walls, by comparison with the observation of Dragoi et al 58 who reported that a simple dehydration treatment at 70 C during 26 hours was not sufficient to retract PEO chains from inside amorphous silica walls.…”

“…58 Indeed, dehydration of PEO moieties obviously reduces their mobility. This again suggests low interaction with the zirconia walls, by comparison with the observation of Dragoi et al 58 who reported that a simple dehydration treatment at 70 C during 26 hours was not sufficient to retract PEO chains from inside amorphous silica walls. The 1 H-13 C CPMAS NMR spectrum of the dehydrated sample (Fig.…”

Controlling the dispersion of ceria using nanoconfinement: application to CeO2/SBA-15 catalysts for NH3-SCR

“…This method was employed for the synthesis of Cu/SBA-15 materials, enabling a good dispersion of copper even at high loadings. 21,22 Yin et al suggested an improved method to use the P123-contained SBA-15 combined with solidstate impregnation methods to avoid the extra step of partial removal of P123, which was applied to the synthesis of CuO/SBA-15 for thiophene capture, 23,24 CeO2/SBA-15 for sulphur capture, 25,26 Pt/SBA-15 for hydrogen storage, 27 Co/SBA-15 for the oxidation of organic pollutants, 28 and Fe/SBA-15 for phenol degradation. 29 Also composite catalysts, i.e., Ag-CeO2/SBA-15, were prepared by using P123-contained SBA-15, showing good dispersion and catalytic performance for roomtemperature reduction of 4-nitrophenol.…”